The present invention relates to a process for producing by sloping etching a thin film transistor with a self-aligned gate with respect to the drain and source thereof and to the transistor obtained by this process.
In general terms, it makes it possible to produce thin film semiconductor components which can be used for the multiplexing of such components arranged in matrix form, as well as for producing charge coupled devices (CCD).
More particularly, it makes it possible to produce thin film transistors (TFT), which can be used in optoelectronics for producing the electronic memory of liquid crystal flat screens. This electronic memory stores the video signal for the duration of the image and is produced in the form of an active matrix of memory points, each being formed from a TFT and a capacitor, whilst being distributed over the entire screen surface. The liquid crystal is in contact with each memory point and is excited for the duration of one image.
A thin film transistor is an insulated gate field effect transistor similar to the MOS transistor (metal-oxide-semiconductor) with the difference that it is produced on an amorphous substrate and not on a monocrystalline silicon wafer. Therefore as they are no longer limited by the size of the crystalline substrate, TFT circuits can have a considerable size.
FR-A2 553 579 discloses a process for the production of a thin film transistor making it possible to align the transistor gate with its drain and source. Unfortunately the edges of the first silicon layer, following the photogravure or photoetching thereof, are vertical and consequently do not provide a good contact and attachment surface for the deposition of a second type n.sup.+ silicon layer with a view to producing ohmic contacts.